The invention relates to actuating apparatus for disc brakes in which elastic sealing elements between the relatively movable spreading members of the actuating apparatus serve the additional function of providing a return force on the spreading members during a brake release.
The return of the spreading elements after a braking action takes place in known actuating apparatus is by means of specially-designed elastomeric seal rings which fulfill two functions, namely the sealing function of the pressure chambers, and the return function after application of the brake.
On fully-lined disc brakes, these two functions may overstress the elastic ring elements on account of the large seal diameter, so that problems can occur in the brake, such as insufficient return of the spreader elements, since the return distance is a function of the elasticity of the ring elements. This can, especially after an automatic adjustment of the clearance of the actuating apparatus caused by wear of the brake lining, lead to a situation where insufficient return results in insufficient brake shoe clearance.